12030-88-5

Rb4O6 and Cs4O6 represent open shell p electron systems, featuring charge, spin, orbital and structural degrees of freedom, which makes them unique candidates for studying the ordering processes related, otherwise exclusively encountered in transition metal based materials. Probing the physical responses has been restrained by the intricacy of synthesizing appropriate amounts of phase pure samples. Tracing the thermal decomposition of respective superoxides has revealed that at least the rubidium and cesium sesquioxides exist in thermodynamic equilibrium, appropriate p-T conditions given. These insights have paved the way to highly efficient and convenient access to Rb4O6 and Cs4O6.

The redox reaction of superoxide (KO2) with highly charged iron porphyrins (Fe(P4+), Fe(P8+), and Fe(P8-)) has been investigated in the ionic liquids (IL) [EMIM][Tf2N] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) a

Kinetic aspects and the mechanism of shaping of particles of potassium superoxide in its synthesis from drops of an alkaline solution of hydrogen peroxide in a flow of a drying agent were studied.

Products of the gas-phase reactions M + N2O and M + O3, where M = Na or K, have been investigated with UV photoelectron spectroscopy and bands have been assigned with the assistance of results from ab initio molecular orbital calculations.For the M + N2O

The title compounds were synthesized at temperatures between 775 and 1175 K from (mostly stoichiometric) mixtures of Fe2O3, elemental rubidium or potassium (A) and their hyperoxides AO2. The structures have been determined by single crystal X-ray diffraction. The alkaline rich ferrate(III) Rb8[Fe2O7] (Cs8[Fe 2O7] structure type, space group P21/c, a = 696.7, b = 1722.1, c = 692.0 pm, β = 119.40°, Z = 2, R1 = 0.0496) exhibits diferrate anions [Fe2O7]8- composed of two vertex-sharing [FeIIIO4] tetrahedra with a linear Fe-O-Fe bridge and nearly ideal 3m symmetry. This is in marked contrast to the Na homologue, where the diferrate anions are decidedly angular. In the series A3[FeO3], the anions in the compounds of the light alkaline cations are chains ∞1[FeO2O 2/2]3-, but similar to the isotypic K6[Fe 2O6] and to CS6[Fe2O6] the new ferrate Rb6[Fe2O6] (K 6Fe2O6 structure type, space group C2/m, a = 741.8(2), b = 1148.7(2), c = 680.08(12) pm, β = 103.65(2)°, Z = 4, R1 = 0.0370) contains isolated binuclear anions [O2FeO 2FeO2]6- composed of two edge sharing [FeO 4] tetrahedra. The new potassium ferrate of the series A 4[Fe2O5], K4[Fe2O 5] (space group P21/c, a = 645.91(14), b = 593.69(13), c = 1003.0(2) pm, β = 103.124(4)°, Z = 4, R1 = 0.0355), constitutes a new structure type, but its structure is still closely related to the Na compound, which crystallizes in the isomorphous subgroup P21/n with a doubled a axis. Both compounds are phylloferrates with layers ∞ 2[Fe2O5]4- consisting of six-membered rings of [FeO4] tetrahedra. In contrast, Rb 4[Fe2O5] contains chains of vertex and edge sharing tetrahedra, so that in both series, A3[FeO3] and A4[Fe2O5], the linkedness of the ferrate tetrahedra increases with the ionic radii of the A counterions.

The reduction of O2 in liquid NH3 at a Pt electrode has been investigated. Chemical and electrochemical measurements show that the first reduction of O2 is a one-electron process producing O2-·, which is a stable species in liquid NH3 and precipitates as KO2 in the presence of K+. The solubility of O2 in liquid NH3 at temperatures between -60 and -40°C was determined, and from these results, the diffusion coefficient of O2 in liquid NH3 was evaluated as 4.4 × 10-5 cm2/s at -55°C.

The unit cell parameters of virgin and thermally treated potassium hexacyanoferrate(II)trihydrate (KFCT) crystals are measured at room temperature. Considerable changes in the lattice constants are observed for as-grown or pre-cooled to the liquid nitrogen temperature samples after heating up to selected higher temperatures for different times. The detected variations may be due to partial or total removal of the three water molecules of crystallization and the transformation of Fe2+ to Fe3+. DSC, DTA and TG are used to study physical and chemical changes associated with the observed crystallographic variations. The effect of γ-irradiation with a dose of 5×105 Gy on the crystal structure of KFCT is also examined. Two computer software programs are used to analyze the data of the X-ray diffraction patterns and the results are compared.

The recombination reaction K + O2 + M was studied by the technique of pulsed photolysis of a K atom precursor followed by time-resolved laser induced fluorescene spectroscopy of K atoms at λ = 404 or 760 nm.Termolecular behavior was demonstrated and absolute third-order rate constants obtained over the temperature range 250-1103 K.A fit of this data to the form AT-n yields k(T,M = N2) = -30>(T/300)-(1.32+/-0.04) cm6 molecule-2 s-1 and k(T,M = He) = -30>(T/300)-(1.22+/-0.07) cm6 molecule-2 s-1.These results are compared to two previous studies of these reactions by different experimental methods, which were in marked disagreement below 600 K.A lower limit of D0(K-O2) > 203 kJ mol-1 is derived.The rate coefficients are then extrapolated from the experimental temperature range to ambient mesopheric temperatures (140 K T 240 K) and to flame temperatures (1500 K T 2200 K), by means of the Troe formalism.Finally, the rates of formation and bond energies of LiO2, NaO2, and KO2 are compared.

A stabilizer for the reaction of KOH and H2O2 yielding potassium superoxide was proposed. The stabilizer does not affect the main consumer properties of the regenerative product based on KO2.

A bibliographical study of the reactions of NaK alloys with their oxides did not explain the related accidents that have occurred in the past, particularly those involving the handling of bubblers installed to remove traces of oxygen and water vapor from blanket gases of LMFR (liquid metal fast reactors). Moreover, it revealed a controversy with respect to the explosive hazard of the NaK alloys + KO2 reaction. A thermodynamic study of the reaction of a NaK alloy with oxygen as well as experimental work on mixtures containing NaK and different oxides (KO2, Na2O, Na2O2) led to the conclusion that violent reactions occurring at ambient temperature, were always linked to the presence of hydrated superoxides or hydroxides. On contact with NaK alloys, these hydrated compounds lead to the formation of hydrogen with a release of heat causing the decomposition of potassium superoxide KO2 and the simultaneous release of oxygen. The oxidation of liquid NaK alloy, by bubbling a mixture of argon and air containing traces of water vapor (H2O 2, besides the hydrated compounds Na2O2·2H2O, NaOH·H2O and KOH·H2O. The gas follows preferential paths and the product obtained is highly heterogeneous in both composition and hardness (porous parts and dense parts). Hydrated superoxide and hydroxides treated under vacuum result in nearly quantitative dehydration after heating at 100 °C. For storage elements or safety valves, containing NaK that has been submitted to slow surface oxidation and hydration, the oxidized layer contains KO2, Na2O2·nH2O and hydrated hydroxides of sodium and potassium. In order to avoid any hazard due to the contact of the oxides with the residual NaK alloy during transport or under impact, it is necessary to freeze the alloy and to reheat it very slowly. Operations such as draining should also be performed slowly, after having calibrated the tanks (temperature and pressure). Therefore the use of NaK liquid alloy to purify gases is questionable; as preferential paths are established, it remains impossible to predict the period of efficiency of a bubbler. Moreover, the NaK alloy does not chemically transform all traces of water vapor; because some remains present in the form of hydrated products, leading to the formation of wastes with a potential hazard during storage or destruction. In our opinion, this method of purification should be abandoned.

Superoxide reductases (SORs) belong to a new class of metalloenzymes that degrade superoxide by reducing it to hydrogen peroxide. These enzymes contain a catalytic iron site that cycles between the FeII and FeIII states during catalysis. A key step in the reduction of superoxide has been suggested to involve HO2 binding to FeII, followed by innersphere electron transfer to afford an FeIII-OO(H) intermediate. In this paper, the mechanism of the superoxide-induced oxidation of a synthetic ferrous SOR model ([FeII- (SMe2N4(tren))]+ (1)) to afford [FeIII(SMe2N4(tren)(solv))]2+ (2-solv) is reported. The XANES spectrum shows that 1 remains five-coordinate in methanolic solution. Upon reaction of 1 with KO2 in MeOH at -90 °C, an intermediate (3) is formed, which is characterized by a LMCT band centered at 452(2780) nm, and a lowspin state (S=1/2), based on its axial EPR spectrum (g⊥ = 2.14; g∥ = 1.97). Hydrogen peroxide is detected in this reaction, using both 1H NMR spectroscopy and a catalase assay. Intermediate 3 is photolabile, so, in lieu of a Raman spectrum, IR was used to obtain vibrational data for 3. At low temperatures, a vo-o Fermi doublet is observed in the IR at 788(2) and 781(2) cm-1, which collapses into a single peak at 784 cm-1 upon the addition of D2O. This vibrational peak diminishes in intensity over time and essentially disappears after 140 s. When 3 is generated using an 18O-labeled isotopic mixture of K18O2/K16O2 (23.28%), the vibration centered at 784 cm-1 shifts to 753 cm-1. This new vibrational peak is close to that predicted (740 cm-1) for a diatomic 18O-18O stretch. In addition, a vo-o vibrational peak assigned to free hydrogen peroxide is also observed (vo-o = 854 cm-1) throughout the course of the reaction between FeII-1 and superoxide and is strongest after 100 s. XAS studies indicate that 3 possesses one sulfur scatterer at 2.33(2) A and four nitrogen scatterers at 2.01(1) A. Addition of two Fe-O shells, each containing one oxygen, one at 1.86(3) A and one at 2.78(3) A, improved the EXAFS fits, suggesting that 3 is an end-on peroxo or hydroperoxo complex, [FeIII(SMe2N4(tren))(OO(H))]+. Upon warming above -50 °C, 3 is converted to 2-MeOH. In methanol and methanol:THF (THF = tetrahydrofuran) solvent mixtures, 2-MeOH is characterized by a LMCT band at λmax = 511(1765) nm, an intermediate spin-state (S = 3/2), and, on the basis of EXAFS, a relatively short Fe-O bond (assigned to a coordinated methanol or methoxide) at 1.94-(10) A. Kinetic measurements in 9:1 THF:MeOH at 25 °C indicate that 3 is formed near the diffusion limit upon addition of HO2 to 1 and converts to 2-MeOH at a rate of 65(1) s-1, which is consistent with kinetic studies involving superoxide oxidation of the SOR iron site.

The high-energy resolution O K-edge absorption near-edge x-ray absorption fine structure spectrum has been measured for in situ prepared potassium superoxide. The experimental data have been analyzed in detail by multiple scattering calculations using self-consistent field potentials. In particular, the so-called ? resonance at the rising edge, which presents a double-peak structure, has been totally resolved and reproduced by the calculations. This analysis indicates that the grown material is arranged in a KO2 structure with an O-O distance between 1.31 and 1.34 A . Moreover, the calculation demonstrates both a complete ionic character of the bound between the O2- anion and K atoms and a strong interaction between the anion and solid-state matrices.